1. Field of the Invention
The present invention relates to an absorption type refrigerating apparatus and particularly to an absorption type refrigerating apparatus capable of maintaining the purity of a refrigerant liquid held in the evaporator to an appropriate level.
2. Description of the Related Art
In an absorption type refrigerating apparatus, the absorbent solution absorbs refrigerant vapor in the absorber thus being diluted. The diluted absorbent solution (diluted solution) is then conveyed to the regenerator where it releases the refrigerant and its concentration is increased. The absorbent solution at a higher concentration is returned back to the absorber. The refrigerant vapor extracted from the absorbent solution is condensed in the condenser and turned to a refrigerant liquid which is then conveyed to the evaporator. The refrigerant liquid conveyed to the evaporator is high in the purity but still contains a trace of the absorbent. The absorbent may be accumulated during a long-run of the operation and gradually decline the purity of the refrigerant liquid in the evaporator.
For avoiding declination of the purity of the refrigerant liquid, it is commonly practiced to withdraw a predetermined amount of the refrigerant liquid in the evaporator and convey it together with the diluted solution to the regenerator. In that case, the more the predetermined amount of the refrigerant liquid in the evaporator, the higher the purity of the refrigerant liquid is gained. However, increasing the predetermined amount of the refrigerant liquid to be withdrawn may lower the efficiency of the operation. As the refrigerant liquid accumulated by consumption of energy for the absorption has been added again to the absorbent solution, the loss of heat (particularly, latent heat) increases.
For minimizing the heat loss, it is proposed that the refrigerant liquid withdrawn from the evaporator is transferred to a rectifier involved in upper part of the regenerator where it is dropped down from the upper end to regain its purity. In that case, the refrigerant liquid is used as a vapor/liquid contact fluid required for the refining. This minimizes the heat loss and increases the efficiency of use of the refrigerant liquid as a primary agent for the absorption type refrigeration. Consequently, the thermal efficiency of the absorption type refrigerating system can be increased. The concentration of the absorbent solution may vary depending on the ambient conditions and the degree of load. Accordingly, if the supply of the refrigerant liquid as the vapor/liquid contact fluid is not properly controlled in response to a change in the concentration of the absorbent solution, the purity of the refrigerant vapor at the top of the rectifier will worsen. For overcoming this problem, it is known to detect the purity of the refrigerant liquid in the evaporator and adjust the supply of the vapor/liquid contact fluid. For example, when the boiling point of the refrigerant liquid in the evaporator is examined and its rise is detected, it is apparent that the purity of the refrigerant liquid worsens.
However, in assuming the deterioration of the purity of the refrigerant liquid from the rise of its boiling point, the supply of the vapor/liquid contact fluid is controlled only after deterioration of the purity of the refrigerant. This delay of action hardly ensures the accurate controlling over the supply. Also, the detection of the rise of the boiling point requires monitoring of both the temperature and the pressure in the evaporator, hence making the controlling procedure complex.